(1) Field of the Invention
The present invention relates to a distance measuring device, and more particularly, to a distance measuring device for measuring a distance to an object having a plurality of markers by obtaining a distance between images of the markers projected on a light receiving section thereof.
(2) Description of the Related Art
In ITS (Intelligent Transport System) etc., for example, a method has been proposed wherein the speed of a vehicle is controlled in such a manner that the distance between the vehicle and one ahead (hereinafter referred to as "preceding vehicle") is always kept constant, to thereby lighten the burden imposed on the driver.
To achieve such control, it is necessary that the distance between the vehicle and the preceding vehicle be measured with accuracy.
Conventionally, a method has been employed in which, for example, two markers are affixed to the rear face of the preceding vehicle and parallax of the markers is optically detected to obtain the distance between the vehicles.
With this method, however, it is difficult to measure with accuracy a wide range of distance from short distance to long distance. Specifically, the visual distance between the markers is small when the markers are viewed from a long distance, and it is therefore desirable that the actual distance between the markers should be significantly large, in order to measure the distance with accuracy. If the actual distance between the markers is large, however, the two markers do not fit in the field of view of a parallax detection camera when viewed from a short distance, and therefore, the markers should desirably be separated at a relatively small distance from each other.
Consequently, a problem of trade-off arises between the long- and short-distance measurements, making accurate measurement difficult.